Old worn or dirty strings can become dull sounding after use and many stories have been told about them. Many players, especially bass players would boil the strings in hot water and make the strings sound brighter again. Basically, they were dislodging the oils and grime that would fill the voids in the string from long hours of performing. This can help to a certain extent but strings that get old stretch and the wrapping or pitch becomes wider and the string loses its clarity and brightness. I have old strings from Hendrix, Clapton, and Beck and laughed about someday cloning them because of their DNA I have in their strings.